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Table 32-67. Verify Backdoor Access Key Command FCCOB Requirements (continued)
FCCOB Number
FCCOB Contents [7:0]
Flash Configuration Field Offset Address
B
Key Byte 7
0x0_0004
After clearing CCIF to launch the Verify Backdoor Access Key command, the flash
memory module checks the FSEC[KEYEN] bits to verify that this command is enabled.
If not enabled, the flash memory module sets the FSTAT[ACCERR] bit and terminates.
If the command is enabled, the flash memory module compares the key provided in
FCCOB to the backdoor comparison key in the Flash Configuration Field. If the
backdoor keys match, the FSEC[SEC] field is changed to the unsecure state and security
is released. If the backdoor keys do not match, security is not released and all future
attempts to execute the Verify Backdoor Access Key command are immediately aborted
and the FSTAT[ACCERR] bit is (again) set to 1 until a reset of the flash memory module
module occurs. If the entire 8-byte key is all zeros or all ones, the Verify Backdoor
Access Key command fails with an access error. The CCIF flag is set after the Verify
Backdoor Access Key operation completes.
Table 32-68. Verify Backdoor Access Key Command Error Handling
Error Condition
Error Bit
The supplied key is all-0s or all-Fs
FSTAT[ACCERR]
An incorrect backdoor key is supplied
FSTAT[ACCERR]
Backdoor key access has not been enabled (see the description of the FSEC register)
FSTAT[ACCERR]
This command is launched and the backdoor key has mismatched since the last power down
reset
FSTAT[ACCERR]
32.4.11 Security
The flash memory module provides security information to the MCU based on contents
of the FSEC security register.
The MCU then limits access to flash memory resources as defined in the device's Chip
Configuration details. During reset, the flash memory module initializes the FSEC
register using data read from the security byte of the Flash Configuration Field (see
Configuration Field Description
).
The following fields are available in the FSEC register. The settings are described in the
Flash Security Register (FTFA_FSEC)
details.
Functional Description
KV4x Reference Manual, Rev. 2, 02/2015
648
Preliminary
Freescale Semiconductor, Inc.
Summary of Contents for freescale KV4 Series
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